1. Field of the Invention
This invention relates to a motor vehicle clutch and, more specifically, to sensing and indicating means for sensing and indicating, respectively, operational parameters, which occur within said clutch. This invention has particular application to sensing the wear condition of the friction pad fixed to a clutch disk within said clutch. Moreover, this invention is useful for sensing and indicating the temperature within the clutch.
2. The Prior Art
Motor vehicle clutches provided with sensing and indicating means for sensing and indicating the degree of wear, i.e. the reduction of thickness of a friction pad fixed to the clutch disk, are known, for example, from German Patent No. 26 40 088. In this known arrangement the clutch disk with its friction pad is, as commonly known, arranged axially between a fly wheel disk and a pressure plate. The pressure plate is mounted for common rotation with the fly wheel disk and axially movable with respect to the fly wheel disk. The clutch disk with the friction pad is accommodated between the fly wheel disk and the pressure plate. The pressure plate is biased in the axial direction toward the fly wheel disk so that the clutch disk is pressure-engaged between the fly wheel disk and the pressure plate. A stationary housing surrounds the fly wheel disk, the clutch disk and the pressure plate. The fly wheel is axially fixed with respect to this housing. The fly wheel disk is connected to a first shaft and the clutch disk is connected to a second shaft. When the clutch disk is pressure-engaged between the fly wheel disk and the pressure plate, the second shaft is entrained by the first shaft. In order to disengage the second shaft from the first shaft, the pressure plate is lifted from the fly wheel disk against the action of the biasing means. In the engaged condition of the clutch, the axial position of the pressure plate with respect to the housing is determined by the thickness of the friction pad on the clutch disk. Therefore, when the friction pad is worn, this axial position of the clutch disk is modified. In order to obtain an indication of the wear condition of the friction pad on the clutch disk, the axial position of the pressure plate is detected. For detecting this axial position, an induction coil is provided on the stationary housing. The pressure plate is provided with a marking element, which determines the inductivity of the induction coil. When the pressure plate is shifted in axial direction due to wear of the friction pad, the position of the marking element with respect to the induction coil is modified. Therefore, the inductivity of the induction coil is also modified and this inductivity can be measured by electrical circuitry. The result of this measurement represents the wear condition of the friction pad.
This known arrangement is not fully satisfactory, because frequently the axial position of the pressure plate is not exclusively dependent on the thickness of the friction pad. Therefore, the position of the pressure plate is not a reliable measure of the wear condition of the friction pad. The position of the pressure plate may be dependent, for example, also on mechanical oscillations occurring in the clutch arrangement. A further disadvantage of the known arrangement is that it is hardly possible to control the wear condition of the friction pad on the whole periphery thereof and to control the wear condition in a plurality of friction pads in cases in which several friction pads are distributed on the clutch disk about the axis thereof. Moreover, it is not possible to observe other operational parameters within the clutch disk which might be of interest, for example the temperature of the clutch disk.